The ability to selectively alter the mammalian genome through gene transfer (transgenic animals), homologous recombination (gene targeting) and chemical mutagenesis is providing new and powerful tools for biomedical research. The production and use of transgenic mice has rapidly expanded since its inception in 1980 and gene targeting, introduced in the late 1980's, is expanding as swiftly. Numbers of transgenic rat stocks, first produced in 1990, are also increasing, albeit more slowly. Scientists have expressed concerns about the preservation, health and free distribution of these animals. Many researchers who produce these animals are not equipped to distribute them widely. The Jackson Laboratory has identified, maintained, preserved, and distributed inbred strains and mutant stocks for over 60 years, and has created a number of supporting genetic resources. Recently the Laboratory established the Induced Mutant Resource (IMR) to import, cryopreserve and distribute biomedically important transgenic, targeted and chemically induced mutant mice. This application seeks funds to extend the IMR's capacity to function as a multicategorical research and service resource for the preservation and supply, of both induced mutant mice and rats. Alternate means of preservation through sperm cryopreservation and ES cell banking will also be developed and employed, to help ensure cost-effective, long-term supply of these important biomedical resources.